Add ingress client

[igalshilman]

This PR adds the first version of a typed client, that can be used outside of restate to communicate with restate backed services/objects .
See examples/ingress.ts for a usage example.

import * as restate from "../src/public_api";
import type { CounterObject, GreeterService } from "./example";

const Greeter: GreeterService = { path: "greeter" };
const Counter: CounterObject = { path: "counter" };

const ingress = restate.ingress.connect({ url: "http://localhost:8080" });

const simpleCall = async (name: string) => {
  const greeter = ingress.service(Greeter);
  const greeting = await greeter.greet(name);

  console.log(greeting);
};

const objectCall = async (name: string) => {
  const couter = ingress.object(Counter, name);
  const count = await couter.count();

  console.log(`The count for ${name} is ${count}`);
};

const idempotentCall = async (name: string, idempotencyKey: string) => {
  const greeter = ingress.service(Greeter);

  // send the request with the idempotent key, and ask restate
  // to remember that key for 3 seconds.
  const greeting = await greeter.greet(
    name,
    restate.ingress.Opts.from({ idempotencyKey, retain: 3 })
  );

  console.log(greeting);
};

const customHeadersCall = async (name: string) => {
  const greeter = ingress.service(Greeter);

  const greeting = await greeter.greet(
    name,
    restate.ingress.Opts.from({ headers: { "x-bob": "1234" } })
  );

  console.log(greeting);
};

const globalCustomHeaders = async (name: string) => {
  const ingress = restate.ingress.connect({
    url: "http://localhost:8080",
    headers: { Authorization: "Bearer mytoken123" },
  });

  const greeting = await ingress.service(Greeter).greet(name);

  console.log(greeting);
};

// Before running this example, make sure
// to run and register `greeter` and `counter` services.
//
// to run them, run:
//
// 1. npm run example
// 2. make sure that restate is running
// 3. restate deployment add localhost:9080

Promise.resolve()
  .then(() => simpleCall("bob"))
  .then(() => objectCall("bob"))
  .then(() => objectCall("mop"))
  .then(() => idempotentCall("joe", "idemp-1"))
  .then(() => idempotentCall("joe", "idemp-1"))
  .then(() => customHeadersCall("bob"))
  .then(() => globalCustomHeaders("bob"))
  .catch((e) => console.error(e));

[slinkydeveloper]

Left a couple of comments.

[slinkydeveloper]

Can you allow to add additional headers?

[igalshilman]

ah!, good idea!

[slinkydeveloper]

A thing I would have done differently is to group the idempotency options all together, like

export interface IdempotencyOptions {
  key: string;
  retain?: number;
}

export interface IngressCallOptions {
  idempotency?: IdempotencyOptions;
  headers: {[string]: string};
}

[igalshilman]

I'd rather to keep it flat for now.

[slinkydeveloper]

This is now number right?

[igalshilman]

This is indeed a number, like the retention number. We said that we would like to align both of them once that feature will be implemented.